There are a few examples of plant diseases caused by protozoa (e.g., Phytomonas, a kinetoplastid). They are transmitted as zoospores that are very durable, and may be able to survive in a resting state in the soil for many years. They have also been shown to transmit plant viruses.
When the motile zoospores come into contact with a root hair they produce a plasmodium and invade the roots.
Some colourless parasitic algae (e.g., Cephaleuros) also cause plant diseases.

Parasitic plants such as mistletoe and dodder are included in the study of phytopathology. Dodder, for example, is used as a conduit either for the transmission of viruses or virus-like agents from a host plant to a plant that is not typically a host or for an agent that is not graft-transmissible.